No abstract

Two new dumbbell-shaped molecules based on two solubilizing and structuring triazatruxene (TAT) units linked by a central chromophore were synthesized and studied. The central chromophore was an electro-deficient fluorene-malononitrile (FM) unit, that can be functionalized symmetrically on two different positions, giving rise to two positional isomers, called TAT-pFM and TAT-mFM, when the TATs are connected to the 2,7-and 3,6-positions, respectively. The two isomers exhibited different electronic conjugation pathways that drastically affect their absorption properties and energy levels. Moreover, while TAT-pFM was organized in a stable 3D mesomorphic structure from room-temperature to the melting point, TAT-mFM remained crystalline and decomposed before melting. Finally, despite a lower hole mobility, the TAT-mFM exhibited the highest Power Conversion Efficiency (PCE) of about 2 % in organic solar cells. This higher PCE was attributed essentially to the pronounced internal charge transfer band contribution to the charge photogeneration observed in TAT-mFM solar cells.